Physical Vapor Deposition (PVD) chambers deposit films on all components surrounding the plasma. Over time, the deposited layer can shed particles that contaminate the substrate being processed. When the process kit undergoes thermal cycling from plasma heating and subsequent cooling while the plasma is off, the deposited film experiences thermal stress that results from the mismatch in the coefficient of thermal expansion (CTE) between the film and the underlying component material. When the stress exceeds the limits of adhesion, particles flake off of the process kit and land on the substrate.
High temperature aluminum PVD chambers can generate aluminum whiskers on the substrate. These whiskers are formed when the process kit surrounding the substrate does not have sufficient time to cool down between subsequent processes. The deposition process heats the substrate significantly more than the heated pedestal. Because the substrate is electrostatically chucked to the pedestal, the wafer is not free to bow under the thermal stress caused by the CTE mismatch between the thick aluminum film and the substrate (e.g., silicon). When the film stress on the substrate gets high enough, whiskers pop out, thus reducing the film stress. The inventors have observed that the temperature of the cover ring and shield play an important role in cooling the substrate via thermal radiation, and in minimizing whisker formation.
Therefore, the inventors have provided an improved process kit.